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GMIRROR(8) FreeBSD System Manager's Manual GMIRROR(8)
NAMEgmirror - control utility for mirrored devices
SYNOPSISgmirrorlabel [-Fhnv] [-bbalance] [-sslice] nameprov...gmirrorclear [-v] prov...gmirrorconfigure [-adfFhnv] [-bbalance] [-sslice] namegmirrorconfigure [-v] -pprioritynameprovgmirrorrebuild [-v] nameprov...gmirrorresize [-v] [-ssize] namegmirrorinsert [-hiv] [-ppriority] nameprov...gmirrorremove [-v] nameprov...gmirroractivate [-v] nameprov...gmirrordeactivate [-v] nameprov...gmirrordestroy [-fv] name...gmirrorforget [-v] name...gmirrorstop [-fv] name...gmirrordumpprov...gmirrorlistgmirrorstatusgmirrorloadgmirrorunloadDESCRIPTION
The gmirror utility is used for mirror (RAID1) configurations. After a
mirror's creation, all components are detected and configured
automatically. All operations like failure detection, stale component
detection, rebuild of stale components, etc. are also done automatically.
The gmirror utility uses on-disk metadata (stored in the provider's last
sector) to store all needed information. Since the last sector is used
for this purpose, it is possible to place a root file system on a mirror.
The first argument to gmirror indicates an action to be performed:
label Create a mirror. The order of components is important,
because a component's priority is based on its position
(starting from 0 to 255). The component with the biggest
priority is used by the prefer balance algorithm and is
also used as a master component when resynchronization is
needed, e.g. after a power failure when the device was
open for writing.
Additional options include:
-bbalance Specifies balance algorithm to use, one
of:
load Read from the
component with the
lowest load. This is
the default balance
algorithm.
prefer Read from the
component with the
biggest priority.
round-robin Use round-robin
algorithm when
choosing component to
read.
split Split read requests,
which are bigger than
or equal to slice size
on N pieces, where N
is the number of
active components.
-F Do not synchronize after a power
failure or system crash. Assumes
device is in consistent state.
-h Hardcode providers' names in metadata.
-n Turn off autosynchronization of stale
components.
-sslice When using the split balance algorithm
and an I/O READ request is bigger than
or equal to this value, the I/O request
will be split into N pieces, where N is
the number of active components.
Defaults to 4096 bytes.
clear Clear metadata on the given providers.
configure Configure the given device.
Additional options include:
-a Turn on autosynchronization of stale
components.
-bbalance Specifies balance algorithm to use.
-d Do not hardcode providers' names in
metadata.
-f Synchronize device after a power
failure or system crash.
-F Do not synchronize after a power
failure or system crash. Assumes
device is in consistent state.
-h Hardcode providers' names in metadata.
-n Turn off autosynchronization of stale
components.
-ppriority Specifies priority for the given
component prov.
-sslice Specifies slice size for split balance
algorithm.
rebuild Rebuild the given mirror components forcibly. If
autosynchronization was not turned off for the given
device, this command should be unnecessary.
resize Change the size of the given mirror.
Additional options include:
-ssize New size of the mirror is expressed in
logical block numbers. This option can be
omitted, then it will be automatically
calculated to maximum available size.
insert Add the given component(s) to the existing mirror.
Additional options include:
-h Hardcode providers' names in metadata.
-i Mark component(s) as inactive
immediately after insertion.
-ppriority Specifies priority of the given
component(s).
remove Remove the given component(s) from the mirror and clear
metadata on it.
activate Activate the given component(s), which were marked as
inactive before.
deactivate Mark the given component(s) as inactive, so it will not
be automatically connected to the mirror.
destroy Stop the given mirror and clear metadata on all its
components.
Additional options include:
-f Stop the given mirror even if it is opened.
forget Forget about components which are not connected. This
command is useful when a disk has failed and cannot be
reconnected, preventing the remove command from being
used to remove it.
stop Stop the given mirror.
Additional options include:
-f Stop the given mirror even if it is opened.
dump Dump metadata stored on the given providers.
list See geom(8).
status See geom(8).
load See geom(8).
unload See geom(8).
Additional options include:
-v Be more verbose.
EXIT STATUS
Exit status is 0 on success, and 1 if the command fails.
EXAMPLES
Use 3 disks to setup a mirror. Choose split balance algorithm, split
only requests which are bigger than or equal to 2kB. Create file system,
mount it, then unmount it and stop device:
gmirror label -v -b split -s 2048 data da0 da1 da2
newfs /dev/mirror/data
mount /dev/mirror/data /mnt
...
umount /mnt
gmirror stop data
gmirror unload
Create a mirror on disk with valid data (note that the last sector of the
disk will be overwritten). Add another disk to this mirror, so it will
be synchronized with existing disk:
gmirror label -v -b round-robin data da0
gmirror insert data da1
Create a mirror, but do not use automatic synchronization feature. Add
another disk and rebuild it:
gmirror label -v -n -b load data da0 da1
gmirror insert data da2
gmirror rebuild data da2
One disk failed. Replace it with a brand new one:
gmirror forget data
gmirror insert data da1
Create a mirror, deactivate one component, do the backup and connect it
again. It will not be resynchronized, if there is no need to do so
(there were no writes in the meantime):
gmirror label data da0 da1
gmirror deactivate data da1
dd if=/dev/da1 of=/backup/data.img bs=1m
gmirror activate data da1
NOTES
Doing kernel dumps to gmirror providers.
This is possible, but some conditions have to be met. First of all, a
kernel dump will go only to one component and gmirror always chooses the
component with the highest priority. Reading a dump from the mirror on
boot will only work if the prefer balance algorithm is used (that way
gmirror will read only from the component with the highest priority). If
you use a different balance algorithm, you should add:
gmirror configure -b prefer data
to the /etc/rc.early script and:
gmirror configure -b round-robin data
to the /etc/rc.local script. The decision which component to choose for
dumping is made when dumpon(8) is called. If on the next boot a
component with a higher priority will be available, the prefer algorithm
will choose to read from it and savecore(8) will find nothing. If on the
next boot a component with the highest priority will be synchronized, the
prefer balance algorithm will read from the next one, thus will find
nothing there.
SEE ALSOgeom(4), dumpon(8), geom(8), gvinum(8), mount(8), newfs(8), savecore(8),
umount(8)HISTORY
The gmirror utility appeared in FreeBSD 5.3.
AUTHORS
Pawel Jakub Dawidek <pjd@FreeBSD.org>
BUGS
There should be a way to change a component's priority inside a running
mirror.
There should be a section with an implementation description.
Documentation for sysctls kern.geom.mirror.* is missing.
FreeBSD 11.0-PRERELEASE December 27, 2013 FreeBSD 11.0-PRERELEASE